Intra-aortic balloon catheter having an ultra-thin stretch blow molded balloon membrane

ABSTRACT

An intra-aortic balloon catheter having an ultra-thin stretch blow molded balloon membrane. The balloon membrane is made from thermoplastic elastomeric and/or semicrystalline materials such as but not limited to polyurethane and polyetheramid.

RELATED APPLICATIONS

This application is a division of, incorporates by reference in itsentirety and claims priority to, application Ser. No. 09/545,763, filedon Apr. 10, 2000, now U.S. Pat. No. 6,213,975 and is acontinuation-in-part of, and claims priority to, application Ser. No.09/188,602, filed on Nov. 9, 1998 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an improved intra-aortic balloon catheter. Moreparticularly, the invention relates to an intra-aortic balloon catheterhaving an ultra-thin stretch blow molded balloon membrane with improvedabrasion resistance, fatigue life, and aneurization resistance.

2. Description of the Prior Art

Intra-aortic balloon (IAB) catheters are used in patients with leftheart failure to augment the pumping action of the heart. The catheters,approximately 1 meter long, have an inflatable and deflatable balloon atthe distal end. The catheter is typically inserted into the femoralartery and moved up the descending thoracic aorta until the distal tipof the balloon is positioned just below or distal to the left subclavianartery. The proximal end of the catheter remains outside of thepatient's body. A passageway for inflating and deflating the balloonextends through the catheter and is connected at its proximal end to anexternal pump. The patient's central aortic pressure is used to time theballoon and the patient's ECG may used to trigger balloon inflation insynchronous counterpulsation to the patient's heart beat.

Intra-aortic balloon therapy increases coronary artery perfusion,decreases the workload of the left ventricle, and allows healing of theinjured myocardium. Ideally, the balloon should be inflating immediatelyafter the aortic valve closes and deflating just prior to the onset ofsystole. When properly coordinated, the inflation of the balloon raisesthe patient's diastolic pressure, increasing the oxygen supply to themyocardium; and balloon deflation just prior to the onset of systolelowers the patient's diastolic pressure, reducing myocardial oxygendemand.

Intra-aortic balloon catheters may also have a central passageway orlumen which can be used to measure aortic pressure. In this dual lumenconstruction, the central lumen may also be used to accommodate a guidewire to facilitate placement of the catheter and to infuse fluids, or todo blood sampling.

Typical dual lumen intra-aortic balloon catheters have an outer,flexible, plastic tube, which serves as the inflating and deflating gaspassageway, and a central tube therethrough formed of plastic tubing,stainless steel tubing, or wire coil embedded in plastic tubing. Apolyurethane compound is used to form the balloon.

All IAB catheters have two opposing design considerations. On the onehand, it is desirable to make the outer diameter of the entire catheteras small as possible: to facilitate insertion of the catheter into theaorta, maximizing blood flow past the inserted catheter, and to allowfor the use of a smaller sheath to further maximize distal flow. On theother hand, however, it is desirable to make the inner diameter of theouter tube as large as possible because a large gas path area isrequired to accomplish the rapid inflation and deflation of the balloon.As a result of these opposing design considerations there is a need fora smaller catheter with a larger gas path area.

One method of making the outer diameter of the wrapped balloon portionof the catheter as small as possible is to wrap the balloon in itsdeflated state as tightly as possible around the inner tube. Wrappingthe balloon tightly, however, has posed a number of difficulties. First,it is difficult to wrap the balloon tightly because of the frictionbetween contacting surfaces of the balloon. Second, contacting surfacesof a tightly wrapped balloon may stick upon initial inflation. DatascopeInvestment Corp.'s co-pending application Ser. No. 08/958,004, filed onOct. 27, 1997, herein incorporated by reference in its entirety,discloses a lubricous coating for the balloon membrane which solves theabove mentioned problems. The coating allows the balloon membrane to bewrapped tightly more easily and prevents sticking of the balloonmembrane upon initial inflation.

A second method of making the outer diameter of the wrapped balloonportion of the catheter as small as possible is to decrease the size ofthe inner tube. Datascope Investment Corp.'s co-pending application Ser.No. 08/958,004 also discloses an intra-aortic balloon catheter with aninner tube having a smaller diameter only in the portion enveloped bythe balloon membrane.

Although the above two methods have substantially reduced the overallinsertion size of the intra-aortic balloon catheter the need stillexists for greater size reduction. Furthermore, the need also exists fora balloon membrane with improved abrasion resistance, fatigue life, andaneurization resistance. Currently, the method of manufacturingpolyurethane balloon membranes is solvent casting. This casting methoddoes not provide the formed membrane with ideal physical and mechanicalproperties. A solvent caste membrane with the basic mechanicalproperties necessary for balloon pumping, typically has a single wallthickness of 4 to 6 mils (a mil is equal to one thousandth of an inch)which leads to a relatively large wrapped diameter of the balloonmembrane. A thin solvent caste polyurethane membrane is capable of beingmanufactured, however, such a membrane does not demonstrate the requiredabrasion resistance and fatigue life. Therefore, the need exists for animproved method of making a balloon membrane which will allow for aballoon membrane having a reduced thickness, and at the same, havingimproved mechanical properties, including an improved abrasionresistance, fatigue life, and aneurization resistance.

The present invention comprises an intra-aortic balloon catheter havinga stretch blow molded balloon membrane. The balloon membrane is madefrom thermoplastic elastomeric and/or semicrystalline materials such asbut not limited to polyurethane and polyetheramid. As discussed above,intra-aortic balloon membranes are generally solvent cast.

The process of stretch blow molding catheter balloon membranes is knownin the art. However, intra-aortic balloons have been traditionally madeby solvent casting because intra-aortic balloon membranes requirespecial characteristics: they must be substantially nondistensible andhave high abrasion resistance, fatigue life, and aneurizationresistance. Stretch blow molding has been traditionally used forangioplasty balloon membranes. These balloons are generally made fromPET, Nylon, or PEBAX materials. These materials achieve their highstrength at least partially because of the crystallization formed intheir microstructure during the initial stretching step of the tube andas a result of quickly cooling the tube to a temperature below thecrystallization temperature of the tube material. Crystallization of themicrostructure increases the strength of the balloon membrane, however,as the inventors of the present invention have discovered, it has anegative effect on the abrasion resistance and fatigue life of theballoon membrane. Given that angioplasty balloon/PTCA therapy is a shortduration therapy, crystallization is generally not a problem. Actually,it is quite useful given that it enhances the strength of the balloonmaterial. Intra-aortic balloon therapy, on the other hand, involvesrepetitive inflation and deflation of the balloon membrane over a longerperiod of time. Accordingly, it is known in the art that stretch blowmolded balloons are not appropriate for intra-aortic balloon membranes,which require high strength as well as high abrasion resistance andfatigue life.

The present invention overcomes the above described obstacle by relyingon the increased strength of polyurethane resulting from the highorientation and molecular interaction of the polyurethane moleculesalong the longitudinal axis of the tube. Said orientation results fromstretching the tube until substantially all stretchability is removed.Polyurethane, and the other materials listed in the present application,do not exhibit significant stress induced crystallization uponstretching. Accordingly, the inventors of the present invention havediscovered a means to create a balloon membrane strong enough to endureintra-aortic balloon pumping therapy without creating crystallizationmicrostructure, which they have discovered, is detrimental to theabrasion resistance and fatigue life of the balloon membrane.

U.S. Pat. No. 5,370,618 to Leonhardt discloses a pulmonary arteryballoon catheter comprising a catheter terminating in a blow moldedpolyurethane balloon membrane. Pulmonary artery catheters are generallyused for blood pressure measurements. Upon insertion and placement ofthe catheter the balloon membrane is inflated, occluding the housingblood vessel, so as to create a measurable pressure differential oneither side of the balloon membrane. In order to achieve completeocclusion of the housing blood vessel the pulmonary artery catheterballoon membrane is elastic so as to allow expansion of the membrane.This is in contrast to the balloon membrane of the present inventionwhich is stretch blow molded and is specifically manufactured tosubstantially eliminate distensibility in the final product.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to produce an ultra-thinintra-aortic balloon membrane with superior abrasion resistance andfatigue life.

It is another object of the invention to produce a method formanufacturing said ultra-thin intra-aortic balloon membrane.

The invention is an intra-aortic balloon catheter having an ultra-thinstretch blow molded balloon membrane. The balloon membrane is made fromthermoplastic elastomeric and/or semicrystalline materials such as butnot limited to polyurethane and polyetheramid.

To the accomplishment of the above and related objects the invention maybe embodied in the form illustrated in the accompanying drawings.Attention is called to the fact, however, that the drawings areillustrative only. Variations are contemplated as being part of theinvention, limited only by the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like elements are depicted by like reference numerals.The drawings are briefly described as follows.

FIG. 1 is longitudinal cross section of a prior art intra-aortic ballooncatheter.

FIG. 1A is a transverse cross section of the prior art intra-aorticballoon catheter taken along line 1A—1A.

FIG. 2 is a longitudinal cross sectional view of a distal portion of theimproved intra-aortic balloon catheter.

FIG. 3 is a side view of a mold having a balloon shaped cavity used tomanufacture the balloon membrane.

FIG. 4 is a top view of the first half of the mold containing andsecuring a stretched tube used as a preform to create the balloonmembrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The general structure of an intra-aortic balloon catheter is bestdescribed in relation to FIGS. 1 and 1A which illustrate a dual-lumenprior art intra-aortic balloon catheter. The catheter 1 is constructedof a plastic outer tube 2 forming a gas passageway lumen 3; and anotherplastic central tube 4 disposed within outer tube 2 and creating acentral passageway or lumen 5 as may best be seen in FIG. 1A.

A balloon 8 is disposed at the distal end of the catheter 1. The distalportion 7 of the central tube 4 extends beyond the distal end 10 ofouter tube 2. The distal end 8A of the balloon 8 is attached to a tip 9formed on the distal end 7 of central tube 4. The proximal end 8B of theballoon 8 is attached, by means of a lap joint, to the distal end 10 ofthe outer tube 2. The distal portion 7 of the central tube 4 supportsthe balloon 8. Said distal portion 7 must have sufficient strength toprevent inversion of the balloon 8 as it inflates and deflates underaortic pressure, but at the same time, be flexible enough to be safelyinserted through an introducer sheath, moved through the arterial tree,and maintained in the thoracic aorta.

The balloon 8 is formed of a nonthrombogenic flexible material, such aspolyurethane, and may have folds 11 formed as a result of wrapping theballoon 8 about the central tube 4 to ease insertion of the catheter 1.The balloon 8 has a single wall thickness of between 4 to 6 mils.Radio-opaque bands 20 at the distal end of the catheter 1 aid inpositioning the balloon 8 in the descending aorta.

Inflation and deflation of the balloon 8 is accomplished through the gaspassageway lumen 3. The central passageway or lumen 5 can accommodate aguide wire for placement or repositioning of the catheter 1. When theguide wire is not disposed in the central passageway or lumen 5, thecentral passageway or lumen 5 may be used for measuring blood pressurein the descending aorta. This pressure measurement may be used tocoordinate the inflation and deflation of the balloon 8 with the pumpingof the heart, however, use of the patient's ECG is preferred.Additionally, the central passageway or lumen 5 may be used to infuseliquids into the descending aorta, or to sample blood.

At the proximal end 12 of the catheter 1 a hub 13 is formed on theproximal end 14 of the outer tube 2. The central passageway or lumen 5extends through the hub 13 and a connector 16 is provided at theproximal end 15 (or exit) of the central passageway or lumen 5.Measurement of aortic pressure and blood sampling may be done throughthe proximal end 15 of the central passageway or lumen 5.

The proximal end 18 of the gas passageway or lumen 3 exits through aside arm 17 of the hub 13 on which is provided a connector 19. Theproximal end 18 of the gas passageway or lumen 3 may be connected to anintra-aortic balloon pump.

The present invention comprises an intra-aortic balloon catheter havingan ultra-thin stretch blow molded balloon membrane. FIG. 2 illustrates alongitudinal cross sectional view of a distal portion of an improvedintra-aortic balloon catheter 30 of the present invention comprising anouter tube 32, an inner tube 33, a tip 34, and an ultra-thinpolyurethane balloon membrane 36. The tip 34 is connected to a distalend of the balloon membrane 36. A distal end of the outer tube 32 isseamlessly welded to a proximal end of the balloon membrane 36. Theballoon membrane 36 has a single wall thickness of between 1 to 2 mils.

The balloon membrane 36 may be made from a variety of thermoplasticelastomeric and/or semicrystalline materials including but not limitedto polyurethane and polyetheramid (known by its trade name as PEBAX,produced by ELF-Atochem of Europe).

Another feature of the invention involves the attachment of the outertube 32 and the balloon membrane 36. The distal end of the outer tube 32is seamlessly welded to the proximal end of the balloon membrane 36. Thedistal end of the outer tube 32 has the same inner and outer diametersas the proximal end of the balloon membrane 36, thus providing a smoothtransition between the two parts without a constriction of the gas path.This is in contrast to the prior art catheter 1 of FIG. 2 in which theproximal end of the balloon 8 and the distal end of the catheter 1 areattached by means of a lap joint. The lap joint is generally compressedduring the manufacturing process in order to assure that the outerdiameter of the lap joint matches that of the outer tube 2. Compressionof the lap joint area leads to a restriction in the gas flow path. Thepresent invention avoids this restriction through the use of a seamlessweld.

FIG. 3 illustrates a side view of a mold 38 with tube clamps 44 on bothsides for securing a tube 46 having ends 50 to the mold 38. The mold 38has a first half 40 and a second half 42 and is utilized in themanufacturing of the ultra-thin balloon membrane 36 to assure therequired profile of said balloon membrane 36. The first half of the mold40 and the second half of the mold 42 together define a balloon shapedcavity 48 illustrated in FIG. 3 as a shadowed segmented line.

The manufacturing process of the balloon membrane 36 comprises thefollowing steps. First, a tube 46, as illustrated in FIG. 4, isstretched to the desired length of the balloon membrane 36. In thepreferred embodiment, and in this example, the tube 46 is 8 inches long,has a wall thickness of 0.02 inches, and is made from polyurethane;however, the tube 46 may be of a different size and may made from otherthermoplastic elastomeric and/or semicrystalline materials or othermaterials that do not display stress induced crystallization or acombination of such materials.

FIG. 4 illustrates a top plain view of the first half 40 of the mold 38which is identical to a view of the mold 38 taken along lines 3A—3A. Theends 50 of the tube 46 are secured by means of the clamps 44 (not shownin FIG. 4 for clarity) to opposite sides of the mold 38. The second half42 of the mold 38, as illustrated in FIG. 3, is attached to the firsthalf of the mold enclosing the stretched tube 46 in the balloon shapedcavity 48.

Stretching the tube 46, approximately two times its original length,prior to blowing orientates the polyurethane molecules along thelongitudinal axis of the tube and substantially eliminates any furtherstretchability of the balloon membrane 36, at internal pressures of twoto four psi, by achieving a high molecular orientation and interaction.Note that this orientation and molecular interaction is achieved withoutsignificant crystallization; this is important to assure improvedabrasion resistance and fatigue life. Significant crystallization isdefined as any amount of crystallization which negatively affects theabrasion resistance and fatigue life of the balloon membrane.Polyurethane and polyetheramid, and other thermoplastic elastomericand/or semicrystalline materials, do not exhibit stress inducedcrystallization. This is in contrast to the materials traditionally usedfor stretch blow molded angioplasty balloon catheter membranes which onaverage have approximately 30% crystallization.

The stretching step assures the substantial nondistensibility of thefinal balloon membrane 36 under balloon inflation pressures ofapproximately 2-4 psi. This is in contrast to the pulmonary arteryballoon catheter, discussed above, whose polyurethane balloon membraneis specifically designed to be distensible so as to allow the membraneto expand, and thereby, occlude the blood vessel in which blood pressureis being measured.

The next manufacturing step involves filling the tube 46 with a gas atapproximately 150 psi, i.e. blowing the tube 46. The amount of pressureapplied depends on the grade of polyurethane: harder materials requirehigher pressure. In all cases, however, the pressure must be sufficientto force the tube 46 to take on the shape of the mold cavity 48. Thetube 46 is then heated above the tube melting temperature whilemaintaining a pressure of 30-40 psi in the tube 46. The final stepinvolves quickly cooling the ballooned tube 46, to a temperature abovethe crystallization temperature of the tube 46, while maintaining apressure of approximately 80 psi in the tube 46. The final thickness ofthe ballooned tube 46, approximately 0.002 inches, is significantlythinner than the prior art thickness of approximately 0.004-0.006inches.

It should be noted that the above detailed manufacturing process ismerely an illustrative example and will vary for different sized tubesand for tubes made of different materials. Manufacturing variablesinclude tube material, tube length, tube thickness, tube diameter, therequired pressure for blowing, the temperature for heating and coolingof the tube, and the amount of pressure maintained in the tube whileheating and cooling the tube.

It should further be noted that balloon membrane of the presentinvention may be used with any variation of intra-aortic ballooncatheters, including an intra-aortic balloon catheter having a co-lumencatheter, i.e. the inner lumen attached to or embedded in the catheterwall, or with any balloon catheter that requires a balloon membrane withimproved abrasion resistance and fatigue life.

What is claimed is:
 1. A method for producing a balloon membrane for anintra-aortic balloon catheter comprising the steps of: a) stretching atube without creating significant crystallization until stretchabilityis substantially eliminated under balloon inflation pressures ofapproximately 2-4 psi; b) blowing the tube by increasing the pressurewithin the tube until the tube has sufficiently ballooned; c) heatingthe ballooned tube to above the melting temperature of the tubematerial; and d) cooling the ballooned tube to above the crystallizationtemperature for the tube material.
 2. The method as claimed in claim 1wherein a pressure above ambient is maintained in the tube while heatingand cooling to maintain the ballooned shape of the tube.
 3. The methodas claimed in claim 1 wherein the tube is at least partially composed ofa thermoplastic elastomeric material.
 4. The method as claimed in claim1 wherein the tube is at least partially composed of a semicrystallinematerial.
 5. The method as claimed in claim 2 wherein the tube is atleast partially composed of a thermoplastic elastomeric semicrystallinematerial.
 6. The method as claimed in claim 2 wherein the tube is atleast partially composed of polyurethane.
 7. The method as claimed inclaim 1 wherein the balloon membrane is at least partially composed ofpolyetheramid.
 8. The method as claimed in claim 1 wherein tube isplaced in a mold having a cavity therein prior to blowing.
 9. The methodas claimed in claims 2, 3, 4, 5, or 6 wherein the tube is stretched toapproximately 2 times its original length.
 10. A method for producing aballoon membrane for an intra-aortic balloon catheter comprising thesteps of: a) stretching a polyurethane tube to approximately two timesits original length; b) placing the tube in a mold having a cavity, saidcavity having the desired balloon profile; c) blowing the tube byincreasing the pressure within the tube until the tube has taken on theshape of the mold; d) heating the ballooned tube to above the meltingtemperature of the tube material while maintaining the pressure in thetube above ambient; and e) cooling the ballooned tube to above thecrystallization temperature for the tube material while maintaining thepressure in the tube above ambient.
 11. The method as claimed in claim10 wherein the tube is stretch without creating significantcrystallization and until stretchability is substantially eliminatedunder balloon inflation pressures of approximately 2-4 psi.